Dormer lead flashing

[jackofairbrother]

Morning people,

Can’t see to find the recommend order to finish my dormer frame to get it water tight

So will have 12mm osb on frame
Breathable membrane
25mm batten for cavity
12mm render carrier board
10mm silicone render

I was going to lap the existing roof membrane up the dormer walls then wrap the dormer frame to overlap this.

Is it best to nail the lead flashing against the membrane or on to the battens. I’ve seen both ways done. Will be concrete interlocking tiles going down after.

I thought nailing against the membrane would be best as I believe the cavity should be vented top and bottom and going on top of the battens would close this?

Thank you!

 

[blup]

You appear to be describing a cold roof approach in which case through ventilation is required,

 

[jackofairbrother]

Hi, it will be a cold roof above but I’m talking about the dormer walls which will have a 25mm battened cavity made off the timber osb frame